Tag Archives: Cassini

Reliving the Titan Descent

A couple of days ago NASA released this gorgeous video constructed from real images taken by the Huygens lander. This revisits Huygen’s successful landing on Titan — Saturn’s largest moon, just over 12 years ago, on January 14, 2005.

Huygens made up half of the Cassini-Huygens joint NASA-ESA (European Space Agency) mission to investigate Saturn and its strange moons. Cassini is currently still in close orbit around Saturn. To date the mission remains the first to successfully land on a moon beyond Earth’s own.

Video: This movie was built thanks to the data collected by ESA’s Huygens Descent Imager/Spectral Radiometer (DISR) on 14 January 2005, during the 147-minutes plunge through Titan’s thick orange-brown atmosphere to a soft sandy riverbed. In 4 minutes 40 seconds, the movie shows what the probe ‘saw’ within the few hours of the descent and the eventual landing. Courtesy: NASA/ESA.

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Tantalizing Enceladus

Fountains_of_Enceladus

Sorry, Moon but my favorite satellite doesn’t even orbit the Earth.

Enceladus is my favorite moon, despite its diminutive size — its diameter is only around 500 km. It circles Saturn and while it only ranks as the ringed planet’s sixth largest moon, it is perhaps the most fascinating.

A decade of images courtesy of the Cassini spacecraft and the Hubble Space Telescope show amazing  plumes of icy material spouting from one or more underground sources. To date, astronomers and planetary scientists have catalogued over 90 geyser-like jets on the surface of Enceladus.

More recently, a couple of year’s ago, NASA’s researchers confirmed the presence of a vast subsurface ocean of liquid water beneath Enceladus’ icy crust. Scientists believe this ocean powers its many geysers or cryovolcanoes. Moreover, the many geysers spew a particle cocktail of ices and organic compounds. It is this mixture of liquid water and organic chemistry that has many scientists agog — pondering the possibility of life beyond the shores of our home planet.

Catch the latest on the search for possible signs of life on Enceladus from Scientific American, here.

Image: Fountains of Enceladus. Recent Cassini images of Saturn’s moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. Courtesy: NASA/JPL/Space Science Institute. Public Domain.

 

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The Transit of Dione

Dione-transit-of-Saturn

This gorgeous image of Saturn’s moon Dione as it transits the gas giant was snapped by the Cassini spacecraft on May 27, 2015. For more beautiful views of the stunning ringed planet and its curious moons visit NASA’s Cassini mission site.

Image: Saturn’s moon Dione transits the giant ringed planet. Courtesy: NASA/JPL-Caltech/Space Science Institute in Boulder, Colorado.

 

 

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Titan Close Up

You could be forgiven for thinking the image below is of Earth. Rather, it is Saturn’s largest moon, Titan, as imaged in infra-red by NASA’s Cassini spacecraft on November 13, 2015. Gorgeous.

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Image: Composite image shows an infrared view of Saturn’s moon Titan from NASA’s Cassini spacecraft, acquired during the mission’s “T-114” flyby on Nov. 13, 2015. Courtesy NASA.

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Pale Blue 2Dot0

IDL TIFF file

Thanks to the prodding of Carl Sagan, just over 25 years ago, on February 14, 1990 to be exact, the Voyager 1 spacecraft turned its camera towards Earth and snapped what has since become an iconic image. It showed our home planet as a very small, very pale blue dot — much as you’d expect from a distance of around 3.7 billion miles.

Though much closer to Earth, the Cassini spacecraft snapped a similar shot of our planet in 2013. Cassini is in its seemingly never-ending orbits of discovery around the Saturnian system, which it began over 10 years ago. It took the image in 2013: Earth in the distance at the center right is dwarfed by Saturn’s rings in the foreground. A rare, beautiful and remarkable image!

Image: Saturn’s rings and Earth in the same frame. Taken on July 19, 2013, via the wide-angle camera on NASA’s Cassini spacecraft Courtesy: NASA/JPL-Caltech/Space Science Institute.

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A Subsurface Anomaly

Enceladusstripes_cassini

Researchers published details of this “subsurface anomaly” in the journal Science, on April 4, 2014. The summary reads as follows:

Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2 = 5435.2 ± 34.9, 106C22 = 1549.8 ± 15.6, 1?) and their ratio (J2/C22 = 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, where M is the mass and R is the radius, suggesting a differentiated body with a low-density core.

In effect this means that the researchers are reasonably confident that an ocean of water lies below the icy surface of Enceladus, one of Saturn’s most intriguing moons.

From NYT:

Inside a moon of Saturn, beneath its icy veneer and above its rocky core, is a sea of water the size of Lake Superior, scientists announced on Thursday.

The findings, published in the journal Science, confirm what planetary scientists have suspected about the moon, Enceladus, ever since they were astonished in 2005 by photographs showing geysers of ice crystals shooting out of its south pole.

“What we’ve done is put forth a strong case for an ocean,” said David J. Stevenson, a professor of planetary science at the California Institute of Technology and an author of the Science paper.

For many researchers, this tiny, shiny cue ball of a moon, just over 300 miles wide, is now the most promising place to look for life elsewhere in the solar system, even more than Mars.

“Definitely Enceladus,” said Larry W. Esposito, a professor of astrophysical and planetary sciences at the University of Colorado, who was not involved in the research. “Because there’s warm water right there now.”

Enceladus (pronounced en-SELL-a-dus) is caught in a gravitational tug of war between Saturn and another moon, Dione, which bends its icy outer layer, creating friction and heat. In the years since discovering the geysers, NASA’s Cassini spacecraft has made repeated flybys of Enceladus, photographing the fissures (nicknamed tiger stripes) where the geysers originate, measuring temperatures and identifying carbon-based organic molecules that could serve as building blocks for life.

Cassini has no instruments that can directly detect water beneath the surface, but three flybys in the years 2010-12 were devoted to producing a map of the gravity field, noting where the pull was stronger or weaker.

During the flybys, lasting just a few minutes, radio telescopes that are part of NASA’s Deep Space Network broadcast a signal to the spacecraft, which echoed it back to Earth. As the pull of Enceladus’s gravity sped and then slowed the spacecraft, the frequency of the radio signal shifted, just as the pitch of a train whistle rises and falls as it passes by a listener.

Using atomic clocks on Earth, the scientists measured the radio frequency with enough precision that they could discern changes in the velocity of Cassini, hundreds of millions of miles away, as minuscule as 14 inches an hour.

They found that the moon’s gravity was weaker at the south pole. At first glance, that is not so surprising; there is a depression at the pole, and lower mass means less gravity. But the depression is so large that the gravity should actually have been weaker.

“Then you say, ‘A-ha, there must be compensation,’ ” Dr. Stevenson said. “Something more dense under the ice. The natural candidate is water.”

Liquid water is 8 percent denser than ice, so the presence of a sea 20 to 25 miles below the surface fits the gravity measurements. “It’s an ocean that extends in all directions from the south pole to about halfway to the equator,” Dr. Stevenson said.

The underground sea is up to six miles thick, much deeper than a lake. “It’s a lot more water than Lake Superior,” Dr. Stevenson said. “It may even be bigger. The ocean could extend all the way to the north pole.”

The conclusion was not a surprise, said Christopher P. McKay, a planetary scientist at NASA Ames Research Center in Mountain View, Calif., who studies the possibility of life on other worlds, but “it confirms in a really robust way what has been sort of the standard model.”

It also makes Enceladus a more attractive destination for a future mission, especially one that would collect samples from the plumes and return them to Earth to see if they contain any microbes.

Read the entire article here.

Image: View of Saturn’s moon Enceladus on July 14, 2005, from the Cassini spacecraft. Courtesy of NASA / JPL / Space Science Institute.

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The View From Saturn

As Carl Sagan would no doubt have had us remember, we are still collectively residents of a very small, very pale blue dot. The image of planet Earth was taken by the Cassini spacecraft, which has been busy circuiting and mapping the Saturnian system over the last several years. Cassini turned the attention of its cameras to our home on July 19, 2013 for this portrait.

From NASA:

Color and black-and-white images of Earth taken by two NASA interplanetary spacecraft on July 19 show our planet and its moon as bright beacons from millions of miles away in space.

NASA’s Cassini spacecraft captured the color images of Earth and the moon from its perch in the Saturn system nearly 900 million miles (1.5 billion kilometers) away. MESSENGER, the first probe to orbit Mercury, took a black-and-white image from a distance of 61 million miles (98 million kilometers) as part of a campaign to search for natural satellites of the planet.

In the Cassini images Earth and the moon appear as mere dots — Earth a pale blue and the moon a stark white, visible between Saturn’s rings. It was the first time Cassini’s highest-resolution camera captured Earth and its moon as two distinct objects.

It also marked the first time people on Earth had advance notice their planet’s portrait was being taken from interplanetary distances. NASA invited the public to celebrate by finding Saturn in their part of the sky, waving at the ringed planet and sharing pictures over the Internet. More than 20,000 people around the world participated.

“We can’t see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Linda Spilker, Cassini project scientist, at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini’s picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth.”

Pictures of Earth from the outer solar system are rare because from that distance, Earth appears very close to our sun. A camera’s sensitive detectors can be damaged by looking directly at the sun, just as a human being can damage his or her retina by doing the same. Cassini was able to take this image because the sun had temporarily moved behind Saturn from the spacecraft’s point of view and most of the light was blocked.

A wide-angle image of Earth will become part of a multi-image picture, or mosaic, of Saturn’s rings, which scientists are assembling. This image is not expected to be available for several weeks because of the time-consuming challenges involved in blending images taken in changing geometry and at vastly different light levels, with faint and extraordinarily bright targets side by side.

“It thrills me to no end that people all over the world took a break from their normal activities to go outside and celebrate the interplanetary salute between robot and maker that these images represent,” said Carolyn Porco, Cassini imaging team lead at the Space Science Institute in Boulder, Colo. “The whole event underscores for me our ‘coming of age’ as planetary explorers.”

Read the entire article here.

Image: In this rare image taken on July 19, 2013, the wide-angle camera on NASA’s Cassini spacecraft has captured Saturn’s rings and our planet Earth and its moon in the same frame. Courtesy: NASA/JPL-Caltech/Space Science Institute.

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Cosmic portrait

Make a note in your calendar if you are so inclined: you’ll be photographed from space on July 19, 2013, sometime between 9.27 and 9.42 pm (GMT).

No, this is not another wacky mapping stunt courtesy of Google. Rather, NASA’s Cassini spacecraft, which will be somewhere in the vicinity of Saturn, will train its cameras on us for a global family portrait.

From NASA:

NASA’s Cassini spacecraft, now exploring Saturn, will take a picture of our home planet from a distance of hundreds of millions of miles on July 19. NASA is inviting the public to help acknowledge the historic interplanetary portrait as it is being taken.

Earth will appear as a small, pale blue dot between the rings of Saturn in the image, which will be part of a mosaic, or multi-image portrait, of the Saturn system Cassini is composing.

“While Earth will be only about a pixel in size from Cassini’s vantage point 898 million [1.44 billion kilometers] away, the team is looking forward to giving the world a chance to see what their home looks like from Saturn,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We hope you’ll join us in waving at Saturn from Earth, so we can commemorate this special opportunity.”

Cassini will start obtaining the Earth part of the mosaic at 2:27 p.m. PDT (5:27 p.m. EDT or 21:27 UTC) and end about 15 minutes later, all while Saturn is eclipsing the sun from Cassini’s point of view. The spacecraft’s unique vantage point in Saturn’s shadow will provide a special scientific opportunity to look at the planet’s rings. At the time of the photo, North America and part of the Atlantic Ocean will be in sunlight.

Unlike two previous Cassini eclipse mosaics of the Saturn system in 2006, which captured Earth, and another in 2012, the July 19 image will be the first to capture the Saturn system with Earth in natural color, as human eyes would see it. It also will be the first to capture Earth and its moon with Cassini’s highest-resolution camera. The probe’s position will allow it to turn its cameras in the direction of the sun, where Earth will be, without damaging the spacecraft’s sensitive detectors.

“Ever since we caught sight of the Earth among the rings of Saturn in September 2006 in a mosaic that has become one of Cassini’s most beloved images, I have wanted to do it all over again, only better,” said Carolyn Porco, Cassini imaging team lead at the Space Science Institute in Boulder, Colo. “This time, I wanted to turn the entire event into an opportunity for everyone around the globe to savor the uniqueness of our planet and the preciousness of the life on it.”

Porco and her imaging team associates examined Cassini’s planned flight path for the remainder of its Saturn mission in search of a time when Earth would not be obstructed by Saturn or its rings. Working with other Cassini team members, they found the July 19 opportunity would permit the spacecraft to spend time in Saturn’s shadow to duplicate the views from earlier in the mission to collect both visible and infrared imagery of the planet and its ring system.

“Looking back towards the sun through the rings highlights the tiniest of ring particles, whose width is comparable to the thickness of hair and which are difficult to see from ground-based telescopes,” said Matt Hedman, a Cassini science team member based at Cornell University in Ithaca, N.Y., and a member of the rings working group. “We’re particularly interested in seeing the structures within Saturn’s dusty E ring, which is sculpted by the activity of the geysers on the moon Enceladus, Saturn’s magnetic field and even solar radiation pressure.”

This latest image will continue a NASA legacy of space-based images of our fragile home, including the 1968 “Earthrise” image taken by the Apollo 8 moon mission from about 240,000 miles (380,000 kilometers) away and the 1990 “Pale Blue Dot” image taken by Voyager 1 from about 4 billion miles (6 billion kilometers) away.

Read the entire article here.

Image: This simulated view from NASA’s Cassini spacecraft shows the expected positions of Saturn and Earth on July 19, 2013, around the time Cassini will take Earth’s picture. Cassini will be about 898 million miles (1.44 billion kilometers) away from Earth at the time. That distance is nearly 10 times the distance from the sun to Earth. Courtesy: NASA/JPL-Caltech

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The Mother of All Storms

Some regions of our planet are home to violent and destructive storms. However, one look at a recent mega-storm on Saturn may put it all in perspective — it could be much, much worse.

From ars technica:

Jupiter’s Great Red Spot may get most of the attention, but it’s hardly the only big weather event in the Solar System. Saturn, for example, has an odd hexagonal pattern in the clouds at its north pole, and when the planet tilted enough to illuminate it, the light revealed a giant hurricane embedded in the center of the hexagon. Scientists think the immense storm may have been there for years.

But Saturn is also home to transient storms that show up sporadically. The most notable of these are the Great White Spots, which can persist for months and alter the weather on a planetary scale. Great White Spots are rare, with only six having been observed since 1876. When one formed in 2010, we were lucky enough to have the Cassini orbiter in place to watch it from close up. Even though the head of the storm was roughly 7,000 km across, Cassini’s cameras were able to image it at resolutions where each pixel was only 14 km across, allowing an unprecedented view into the storm’s dynamics.

The storm turned out to be very violent, with convective features as big as 3,000 km across that could form and dissipate in as little as 10 hours. Winds of over 400 km/hour were detected, and the pressure gradient between the storm and the unaffected areas nearby was twice that of the one observed in the Great Red Spot of Jupiter. By carefully mapping the direction of the winds, the authors were able to conclude that the head of the White Spot was an anti-cyclone, with winds orbiting around a central feature.

Convection that brings warm material up from the depths of Saturn’s atmosphere appears to be key to driving these storms. The authors built an atmospheric model that could reproduce the White Spot and found that shutting down the energy injection from the lower atmosphere was enough to kill the storm. In addition, observations suggest that many areas of the storm contain freshly condensed particles, which may represent material that was brought up from the lower atmosphere and then condensed when it reached the cooler upper layers.

The Great White spot was an anticyclone, and the authors’ model suggests that there’s only a very narrow band of winds on Saturn that enable the formation of a Great White Spot. The convective activity won’t trigger a White Spot anywhere outside the range of 31.5° and 32.4°N, which probably goes a long way toward explaining why the storms are so rare.

Read the entire article here.

Image: The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Courtesy of NASA/JPL.

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Rivers of Methane

The image shows what looks like a satellite picture of a river delta, complete with tributaries. It could be the Nile or the Amazon river systems as seen from space.

However, the image is not of an earthbound river at all. It’s a recently discovered river on Titan, Saturn’s largest moon. And, the river’s contents are not even water, but probably a mixture of liquid ethane and methane.

From NASA:

This image from NASA’s Cassini spacecraft shows a vast river system on Saturn’s moon Titan. It is the first time images from space have revealed a river system so vast and in such high resolution anywhere other than Earth. The image was acquired on Sept. 26, 2012, on Cassini’s 87th close flyby of Titan. The river valley crosses Titan’s north polar region and runs into Ligeia Mare, one of the three great seas in the high northern latitudes of Saturn’s moon Titan. It stretches more than 200 miles (400 kilometers).

Scientists deduce that the river is filled with liquid because it appears dark along its entire extent in the high-resolution radar image, indicating a smooth surface. That liquid is presumably ethane mixed with methane, the former having been positively identified in 2008 by Cassini’s visual and infrared mapping spectrometer at the lake known as Ontario Lacus in Titan’s southern hemisphere. Though there are some short, local meanders, the relative straightness of the river valley suggests it follows the trace of at least one fault, similar to other large rivers running into the southern margin of Ligeia Mare (see PIA10008). Such faults may lead to the opening of basins and perhaps to the formation of the giant seas themselves.

North is toward the top of this image.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The RADAR instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries. JPL is a division of the California Institute of Technology in Pasadena.

Read the entire article following the jump.

Image courtesy of NASA/JPL-Caltech/ASI.

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